Joubert Syndrome and related disorders (JSRD) are a group of autosomal recessive conditions characterized by a distinctive hindbrain malformation (the molar tooth sign - MTS) combined with intellectual disability (mental retardation), hypotonia, ataxia, and variably, cystic renal disease, retinal dystrophy and hepatic fibrosis. The overall context of the project is to explore the role of the primary cilium/basal body (PC/BB) in the development/function of the brain and retina. Specifically, we propose to study the molecular function of CC2D2A, a newly discovered gene responsible for JS, and to identify additional components of the genetic/protein network underlying JSRD using several highly informative families. In Aim 1, we will investigate CC2D2A function by determining temporal, spatial and subcellular expression as well as identifying additional proteins that interact with CC2D2A. In Aim 2, we will use the cc2d2a photoreceptor phenotype in zebrafish to dissect the molecular function of Cc2d2a and model oligogenic inheritance by examining the effects of JSRD gene mutants/morphant combinations. Given that <50% of JSRD patients have mutations in the known genes, the goal of Aim 3 is to identify additional components of the genetic/protein network responsible for JSRD. This work has broad implications for human disease. Most specifically, it will enhance our understanding of the development/function of the brain, retina and kidney, provide improved diagnostic and prognostic information for patients with JSRD and potentially identify molecular targets for therapies to prevent or delay the progressive retinal, kidney and liver disease seen in JSRD and other ciliopathies. Given the protean role of the PC/BB in cellular function and Mendelian diseases, combined with the emerging associations between PC/BB genes and more common neurological diseases such as schizophrenia and autism, this work is also likely to reveal mechanisms underlying common diseases of the brain, retina, kidney and other tissues.